Serological Distinctions Between the Viruses of Encephalitis in St. Louis,1933,Equine Encephalomyelitis,and Vesicular Stomatitis. ∗

Abstract

The problem of the immunological relationship of the viruses of the encephalitis prevailing in St. Louis and Kansas City in 1933 and the viruses of equine encephalomyelitis and vesicular stomatitis has been studied by a series of cross-protection tests with the viruses associated with these diseases and their respective immune sera. A mouse strain of encephalitis virus obtained from Webster and Fite, 1 a neurotropic guinea pig strain of equine encephalomyelitis virus of the western type, 2 as well as similar mouse strains of the New Jersey and Indiana types 3 of vesicular stomatitis virus were employed, together with antisera from a monkey convalescent from experimental encephalitis, antisera from a rabbit and a horse convalescent from encephalomyelitis of the eastern type, 4 serum from a rabbit immunized against the western type of encephalomyelitis virus, and similar sera from rabbits immunized against the 2 strains of vesicular stomatitis virus.

Hormone broth suspensions of the stomatitis and encephalitis materials were mixed with equal volumes of antisera so as to make final dilutions of 10^-3, 10^-4, 10^-5, and 10⁻⁶. In the case of encephalomyelitis material, final dilutions of only 10^-3 and 10^-4 were used. Normal rabbit serum was substituted for antisera in similar series as controls. The mixtures were incubated at 37.5°C. for 2 hours, placed in the icechest overnight, and then examined for the presence of virus by intracerebral injection into animals.† For the stomatitis and the encephalitis virus mice were employed, and for the encephalomyelitis virus guinea pigs.

The results as tabulated showed that a particular virus was neutralized only by its homologous antiserum. Hence no cross-immunity reactions occur between any of the viruses studied. Webster and Fite 1 have stated that the results of animal inoculation tests indicate that encephalitis virus is not related to equine encephalomyelitis or vesicular stomatitis viruses. The results of the serological tests here reported are in accord with their observations.